if you drop a piece of food on the ground (most likely, something that you've taken a long time to prepare, at a time of crisis right before this needs to be served, or after a long day), you have 5 seconds to pick it up and it will be fine. While it still has germs, these 3 words just may give you peace of mind.

Crap! I just dropped the souffle I've been working on for 3 hours! And Jackie is getting here in 5 minutes! *picks it up* 5 second rule will have to do I guess.

When stuff you are eating falls on the floor, you have two options. You can pick it up and eat it, or you can throw it out. The five second rule is used when what ever falls is tasty, but you dont want to gross out your friends by eating something dirty. The five second rule, when imposed (usually along with a quick rinse or blow off) makes what ever you still want to eat socially acceptable to eat and void of all dirtyness. The 5 second rule may be be changed to the 10 second rule, the 15 second rul, or the "i have no clue how long its been there" rule.

guy one: dude, you just dropped your good tasting stuff
guy two: aww crap, butter move fast to make the five second rule. This stuff sure isnt good enough for a ten-er or a 15-er.